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Radio frequency identification (RFID) systems at ultra high frequencies operate in an environment exposed to fading. While state-of-the-art RFID readers utilise multiple receive antennas with antenna multiplexing in order to deal with the multipath propagation environment, this contribution proposes maximal ratio combining at RFID reader receivers. A dual receive antenna RFID reader is presented in this paper. The composition of the receive signal and the constellation in the I/Q plane on each antenna is analysed and discussed thoroughly. With that knowledge, we design a receiver estimating the channel coefficients and realising maximal ratio combining of the received signals, thus achieving the optimum combination of receive signals in terms of SNR maximisation. Underlying assumptions on the receive signals at the RFID reader for the design of the receiver have been cross-verified with measurements. Furthermore, the receiver has been implemented on an FPGA and functionally verified.
Date of Conference: 24-25 Sept. 2009